As IP networks become the dominant networks of carriers, the demand on IP network-based services becomes more urgent. At present, Multiprotocol Label Switching, L2 Virtual Private Network (MPLS L2VPN) technology can provide IP service and Layer 2 VPN service simultaneously on the same network, and has features of being able to set any rate conveniently as well as simple configuration. Using this technology, carriers may provide various services such as IP service, Layer 3 VPN, Layer 2 VPN, Traffic Engineering and Differentiated Service (Diffserv) on the same network. As a result, for carriers the cost of construction, maintenance and operation can be reduced drastically.
MPLS L2VPN includes Virtual Private LAN Service (VPLS) and Virtual Leased Line (VLL).
VPLS is a kind of Layer 2 VPN, and the existing VPLS mainly has two drafts: draft-ietf-l2vpn-vpls-bgp-XX and draft-ietf-l2vpn-vpls-ldp-XX. Wherein, draft-ietf-l2vpn-vpls-ldp-XX defines a hierarchical VPLS, i.e. HVPLS in Virtual Private LAN Service Label Distribution Protocol (VPLS LDP) mode, while draft-ietf-l2vpn-vpls-bgp-XX does not designate the solution to realize a hierarchical model in Border Gateway Protocol (BGP) mode.
In HVPLS of VPLS LDP mode, VPLS networks can be connected with each other, so that VPLS service of a larger scale is established. Fully connected VPLS networks are connected with each other via a single Label Switch Path (LSP) tunnel, and in each VPLS network, two domains are connected via one or more (which is a backup scheme) Pseudo Wires (PWs). This solution requires that the whole VPLS network should belong to the same autonomous system.
The characteristic of HVPLS solution in VPLS LDP mode lies in that a Fully connected tunnel LSP is established among all Provider Edge routers (PEs) that provide VPLS service. For each VPLS service, n*(n−1)/2 PWs should be established among n PEs. These PWs may be generated via a signaling protocol. In this scheme, PEs providing Virtual Circuits (VCs) need to duplicate data packets; and for first packet, broadcast packet and multicast packet, each PE equipment needs to broadcast the packet to all of the connected equipment. Although the total number of broadcast packets duplicated remains the same, the broadcast packets are accomplished by a plurality of equipment in the HVPLS, thus the burden of signaling protocol and data packet duplication can be reduced via hierarchical connection.
In HVPLS of VPLS LDP mode, an ISP (Internet Service Provider) will usually place some small PEs to the customer agglomerations and converge these small PEs to a PE in the central office. Therefore, it is a requirement to extend the tunneling technology in VPLS service to Multi Tenant Units (MTUs), thus the MTUs may be regarded as PE equipment, and a basic VPLS pseudo connection service is provided on the edge of each MTU. Feasible technologies include employing pseudo connection and Q-in-Q (directly using tunneling protocols encapsulated by an Ethernet switch on the basis of 802.1 q) logic interface between an MTU and a PE. In a hierarchical VPLS with two hierarchies, one hierarchy is the core PW of the VPLS, and the other is an extended access PW.
There are two access modes between the two hierarchies of HVPLS, wherein one access mode is MPLS Edge HVPLS (ME-HVPLS), the other is Ethernet Edge HVPLS (EE-HVPLS).
The networking structure of ME-HVPLS mode is shown in FIG. 1:
CE1, CE2 and CE3 are Customer Edge routers, SPE1, SPE2 and SPE3 are Service Provider-end Provider Edge routers, and UPE means User-end Provider Edge router, which, as a converge device, only establishes a pseudo connection access link U-PW with SPE1 and establishes a U-PW backup link with SPE2. In other words, it will not establish any pseudo links with any other opposite end. In such a networking mode, the data forwarding process is as follows: a UPE forwards a packet sent from CE1 to SPE1 after placing an MPLS label corresponding to U-PW on the packet, and at the same time, SPE1 determines the Virtual Switch Instance (VSI) to which the packet belongs according to the multiplexing separation label, and then forwards the packet after placing a multiplexing separation label corresponding to N-PW on the packet according to the destination Medium Access Control (MAC) address of the user packet. After SPE1 receives a packet sent from the N-PW side, it sends the packet to the UPE after placing a multiplexing separation label corresponding to U-PW on the packet. Then, the UPE forwards the packet to CE1.
If CE1 and CE2 are local CEs, when data exchange is needed between CE1 and CE2, because the UPE has a bridge function inherently, it performs packet forwarding between CE1 and CE2 directly, rather than delivering the packet upward to SPE1. However, for a first packet or a broadcast packet of which the destination MAC address is unknown, the UPE will still forward the packet to SPE1 via the U-PW at the same time when it forwards the packet directly between CE1 and CE2 via bridging broadcast, and SPE1 duplicates the packet and forwards it to each opposite CE.
Because the PW connected between a UPE and an SPE requires an LSP tunnel established on the basis of LDP and Interior Gateway Protocol (IGP) jointly, if the whole VPLS network does not belong to an autonomous system, because IGP cannot be operated, the tunnel cannot be established via IGP and LDP jointly and a PW cannot be established between two hierarchies of an HVPLS. In other words, the solution is not applicable for the case in which the whole VPLS network does not belong to an autonomous system.